One of the key features of Islamist ideology is that it categorises people by religion rather than by nationality. Though this is far from the only reason for its anti-semitism, it is an important factor in the mix, and helps to explain a great deal. Because Israel is a Jewish state, at least in terms of the inspiration that created it, all Jews are seen, in Islamist eyes, as indistinguishable from Israelis. They thus become targets for terror worldwide.

This way of thinking is all but incomprehensible to most modern British people, used as we are to living in one of the world’s older nation states. It is thus at the heart of the furore over Shamima Begum. To her, and to the ISIS fanatics who groomed her, the United Kingdom has no claim on her loyalty. Hence her departure to Syria in in 2014, her marriage to a ISIS terrorist, and so on. That people can grow up in Britain without feeling any obligation to it stirs, in most of us, a sense of disgust, bewilderment and danger. To ISIS and the Islamists, it is the most natural thing in the world.

All this helps to explain why our treason laws need to be modernised, made effective – and used. For although the concept of loyalty to our country comes naturally to us, its expression has fallen out of use in our legal system. Bringing it back in an improved form has been proposed by Richard Ekins for Policy Exchange. His ideas are backed by, among others, a former Lord Chief Justice (Lord Judge), a former head of MI5 (Lord Evans), a former Home Secretary (Amber Rudd) and a former head of former head of counter-terrorism at Scotland Yard (Richard Walton).

An updated treason law would help to solve the problem of what to do with ISIS terrorists and their supporters who are British nationals. Sajid Javid and David Gauke have illustrated the institutional polarities of the current debate. Javid, whose focus is on security, says that Begum shouldn’t come back to Britain. Gauke, whose focus is on the integrity of the legal system, says that she can’t be kept out. These tensions help to illustrate a wider point. At present, the policy on ISIS backers and terrorists returning from the Middle East seems to be: hope they don’t come back; hope we can spot those that do; attempt to deradicalise these – and cross one’s fingers for luck.

There will always be problems in identifying people who have slipped away to Syria and now seek to slip back, and in gathering evidence for prosecution here under present laws. It would be preferable for those who have committed crimes abroad to be charged abroad. But a treason law would fill an important legal gap. If there’s enough evidence for the likes of Begum to be charged, then they should be charged. If there isn’t, then the combination of security surveillance and deradicalisation programmes must do, when appropriate. At any rate, the reshaping of our treason law is well overdue.

One thinks easily of the need as justice-related, and as security-related, too. But strange though it may sound, a modern treason law would be a powerful instrument of community cohesion. Word of it would get about, even to people and communities who don’t speak English at all, and thus aren’t integrated. The idea that one owes a loyalty to the country in which one lives would be furthered. It is its absence that helped to create Begum.